Sen. Dick Durbin said any such move by Trump would be quickly contested.

“He’ll face a challenge, I’m sure, if he oversteps what the law requires when it comes to his responsibility as commander in chief,” Durbin of Illinois said on CBS’ “Face the Nation.”

“I can just tell you, I don’t know what he’s basing this on, but he’s faced so many lawsuits when he ignores the law and ignores tradition and precedent and just goes forward without any concern,” Durbin, the Senate majority whip, added.

Rep. Adam Smith, the chairman of the House Armed Services Committee, said the “short answer” is that Trump has the authority to declare an emergency but that the president would have to prove one exists on the border.

“There is a provision in law that says the president can declare an emergency. It’s been done a number of times. But primarily it’s been done to build facilities in Afghanistan and Iraq. And in this case I think the president would be wide open to a court challenge saying, ‘Where’s the emergency?’ You have to establish that in order to do this,” Smith of Washington said on ABC’s “This Week.”

He said it would be a “terrible use” of funds from the Department of Defense.

“The president spends most of his time talking about how we’re not spending enough on national security. Now he wants to take $20 billion dollars out of the defense budget to build a wall, which by the way is not going to improve our border security.”

Trump, speaking during a news conference after meeting with congressional leaders at the White House over the partial government shutdown, signaled that he might use the maneuver to bypass Congress.

“Absolutely, we could call a national emergency because of the security of our county,” Trump said last Friday. “I haven’t done it. I may do it.”

He and Congress are deadlocked over funding for his border wall, which he now says could be made of either concrete or steel slats.

Trump is demanding $5.6 billion but Democrats have offered only $1.3 billion for border security – and nothing for a wall.

The stalemate has left the government partially closed, with about 800,000 federal employees either on furlough or working without pay.